Continuous casting apparatus with electromagnetic screen

ABSTRACT

AN APPARATUS FOR CONTINUOUS AND SEMICONTINUOUS CASTING OF METALS PERMITTING INGOTS TO BE PRODUCED WITHOUT ANY SURFACE DEFECTS DUE TO THE FACT THAT A MAGNETIC FIELD IS PROVIDED IN THE APPARATUS DISTRIBUTED IN THE AXIAL DIRECTION SO AS TO ENSURE THE QUALITY OF THE HYDROSTATIC AND ELECTROMAGENTIC PRESSURES. THIS IS ACHIEVED BY MEANS OF AN ELECTROMAGNETIC SCREEN MOUNTED WITHIN THE RING-SHAPED INDUCTOR. THE ELECTROMAGNETIC SCREEN CONSISTS OF A CLOSED RING OF A NON-MAGNETIC METAL WHOSE THICKNESS INCREASES UPWARDLY WHILE THE LOWER EDGE IS DISPOSED AT APPROXIMATELY HALF OF THE HEIGHT OF THE INDUCTOR.

"mg'tm z. N; GETSELEV 3,605,865

CONTINUOUS CASTING APPARATUS WITH ELECTROIAGIETIC SCREEN N v Q & =5 t kFIG.

United States Patent 3,605,865 CONTINUOUS CASTING APPARATUS WITHELECTROMAGNETIC SCREEN Zinovy Naumovich Getselev, Prospekt Metallurgov32,

. kv. 11, Kuibyshev, U.S.S.R. Filed Dec. 23, 1969, Ser. No. 887,646 Int.Cl. B22d 11/10, 27/02 US. Cl. 164-250 2 Claims ABSTRACT OF THEDISCLOSURE An apparatus for continuous and semicontinuous casting ofmetals permitting ingots to be produced without any surface defects dueto the fact that a magnetic field is provided in the apparatusdistributed in the axial direction so as to ensure the quality of thehydrostatic and electromagnetic pressures. This is achieved by means ofan electromagnetic screen mounted within the ring-shaped inductor. Theelectromagnetic screen consists of a closed ring of a non-magnetic metalwhose thickness increases upwardly while the lower edge is disposed atapproximately half of the height of the inductor.

The present invention relates to apparatus for continuous andsemicontinuous casting of metals.

Known in the art are apparatus provided with a ringtype electromagneticinductor, a device for uniformly feeding molten metal into this inductorand a device for feeding a cooling medium into the gap between theinductor and the lateral surface of the ingot being cast.

The ring-shaped inductor is employed for exciting an alternatingelectromagnetic field around the molten metal fed into the ingot-formingzone, the said electromagnetic field developing forces directed into themolten metal and preventing it from spreading, thus forming this metal.In this case the molten metal acquires a required shape in the crosssection as well as required overall dimensions. A cooling liquid isapplied onto the lateral surface of the column of molten metal formed bythe electromagnetic field and, as a result, the metal being cooledcompletely solidifies during the movement and forms an ingot.

In the process of forming the ingot defects often appear on the surfacethereof due to a distortion of the shape and dimensions of the ingot,for example, longitudinal pleats and transverse waves.

The above defects take place in the case of disparity between thehydrostatic pressure of the molten metal and the electromagneticpressure on the lateral surface of the molten zone of the ingot.

Furthermore, the longitudinal pleats may result from a high intensity ofmovement of the molten metal caused by the electromagnetic forcesshaping the ingot.

The object of the invention is to provide an apparatus for continuousand semicontinuous casting of metals, in which the distribution of themagnetic field in an axial direction is such that the hydrostaticpressure on the lateral surface of the liquid zone of the ingot is equalto the electromagnetic pressure, while the magnetic field in the upperportion of the liquid zone is such that it does not lead to an intensivemovement of the metal inside of the liquid zone of the ingot, and thismakes it possible to produce ingots without defects on their surface.

This and other objects of the invention are attained by providing anapparatus for continuous and semicontinuous casting of metals in which,according to the invention, arranged inside the ring-shapedelectromagnetic inductor coaxially therewith is an electromagneticscreen comprising a closed ring of non-magnetic metal featuring anupwardly increasing thickness, whereas the lower edge 3,605,855 PatentedSept. 20, 1971 of the screen is located at approximately half of theheight of the inductor.

In some cases a ring made of a metal having high electric conduction ispreferably positioned inside the electromagnetic screen concentricallyand close thereto, said ring being arranged near the upper portion ofthe screen and being capable of moving along a vertical line.

Further objects and advantages of the invention will be apparent fromthe following description of the invention, reference being made to theaccompanying drawings, in which:

FIG. 1 shows a longitudinal section of the apparatus for continuous andsemicontinuous casting of metals; and

FIG. 2 shows a diagram of distribution of the electromagnetic andhydrostatic pressures on the lateral side of the ingot within the liquidzone.

The apparatus shown in the drawings consists of a horizontally arrangedring-shaped electromagnetic inductor 1 (FIG. 1), a feed tray 2communicating with a tank 3, in the bottom of which there is provided ahole 4 of a device disposed under the tank 3 and employed for a uniformdistribution of an aluminium melt, which device consists of a cup 5 witha cone 6 in the centre of the bottom and with openings 7 uniformlydistributed over its side walls 8, a pan 9 located under the cup 5, acollector 10, screw elevators 11 for moving the apparatus in a verticaldirection, an electromagnetic screen 12 located inside the inductor 1and arranged coaxially therewith, a ring 13 made of a material havinghigh electric conduction and located inside the screen 12.

The electromagnetic screen 12 is a closed ring whose cross section isfeatured by an upwardly increasing thickness, said screen being made ofa non-magnetic metal. The conduction of the screen material is selecteddepending on the current frequency. For example, at a frequency of 1000to 2500 c./s., the screen is to be made of nonmagnetic steel having ahigh specific resistance, while at a frequency of 50 to 500 c./s. thescreen is to be made of aluminium or copper. The lower edge 14 of thescreen 12 is located approximately at the level of half of the height ofthe inductor and has a minimum thickness of 1 to 1.5 mm.

The thickness of the screen 12 is changed along the height depending onthe distribution of the magnetic field of the inductor 1 in an axialdirection.

The ring 13 is located in the upper portion of the screen 12concentrically and close thereto.

The ring 13 is made of a copper tube having a rectangular cross sectionand is capable of moving along a vertical line. The ring 13 is cooled bywater.

The above-described apparatus operates as follows.

The molten aluminium is fed through the tray 2 and opening 4 in the tank3 into the pan 9 inserted into the inductor 1 from below. The water usedas a cooling medi um and fed from the collector 10 through the annularnozzle 15, formed by the electromagnetic screen 12 on one side and bythe wall of the ring-shaped collector 10 on the other side, is fed intothe pan 9 along the outer surface of the screen 12 and cools the moltenmetal located on this pan so that the metal begins to solidify.

In the drawing A stands for the solidified portion of the melt and Bstands for non-solidified (liquid) portion of the melt.

The electromagnetic field produced by the inductor 1 develops forces inthe melt due to which the liquid portion B of the ingot is preventedfrom spreading and in its form assumes the shape of the inductor incross section.

Together with an increase in the column of the metal shaped, partiallysolidified and disposed on the pan 9, the latter starts to move down. Atthis moment the cup 5 is set on the upper surface of the molten metal(portion B).

The molten metal occurring on the cone 6 of the cup spreads along itsbottom and through openings 7 is uniformly supplied into the inductor 1.

The molten metal fed into the inductor is shaped and solidified forminga column of a solid metal which moves down together with the pan. Thesolidification takes place when the water is fed directly on the lateralsurface of the ingot.

In the process of casting due to unavoidable changes in the rate ofcasting, intensity of cooling, position of the cooling band anddeflection of the ingot from a vertical axis, the boundary between theliquid portion B and solid portion A of the ingot can be displaced overthe surface of the ingot (along the axes aa and bb in FIG. 1).

The displacement of this boundary always occurs at the beginning of theprocess of casting.

As known, the hydrostatic pressure P of the liquid portion B within themetal melt is changed linearly (a straight line 16 in FIG. 2). At thesame time, the calculations and experiments have shown that according tothe character of distribution of the magnetic field, the electromagneticpressure P acting on the surface of the liquid portion B along the axis0-2 at all points exceeds the hydrostatic pressure P (curve 17). In thiscase, the more distant is any point of the surface of the liquid portionof the ingot from the boundary between the liquid and solid portions ofthe ingot, the greater is the difference between the above-saidpressures.

The disparity between the hydrostatic and electromagnetic pressures onthe lateral surface of the liquid portions of the ingot results in thefact that at any displacements of the boundary between the liquid B andsolid A portions of the ingot (axis 0-11 in FIG. 1), the transversedimensions of the liquid portion, that is of the ingot, are changed. Forexample, if this boundary is displaced upwards due to the fact that theelectromagnetic pressure exceeds the hydrostatic pressure, the shapedportion of the ingot tends to squeeze and this results in a reduction ofthe transverse dimensions of the ingot.

Due to the reduction of the diameter of the ingot during its downwardmovement in the process of casting, the cooling band is displaced belowits initial position.

In this case the boundary between the liquid and solid portions of theingot is also lowered, i.e. it will occupy the position close to theinitial position, whereas the diameter of the ingot will assume thedimensions close to the initial size. Due to such variations in thetransverse dimensions, the surface of the ingot becomes wave-shapedwhile the dimensions exceed the permissible value.

Owing to the fact that the screen 12 is ring-shaped with upwardlydirected thickening, the rate of attenuation of the magnetic field ofthe inductor 1 is increased upwardly. In this case the magnetic field isdistributed so that the electromagnetic pressure is changed linearlyalong the height'of the liquid portion of the ingot and this providesfor the equality between the hydrostatic and electromagnetic pressures.

The equality of these pressures on the surface of the liquid portion Bof the ingot being cast makes it possible to avoid any disturbance ofits shape, e.g. formation of transverse waves and a change of thedimensions of the ingot.

In the process of shaping the ingot there may be observed intensivemovement of metal within the liquid portion B of the ingot due to theelectromagnetic forces excited by the inductor 1.

In this case the flows of metal carry the solidified crystals from thetransition zone (zone of volume solidification) onto the surface of theingot. These crystals are concentrated on the lateral surface of theingot under the action of the hydrostatic and electromagnetic forces,and this results in the layers of the liquid portion of the ingotadjacent the surface acquiringa semi-liquid (pulpy) state.

In the process of Shaping the metal in such a state, longitudinal pleatsare formed on the surface of the metal. After the solidification of themetal, the pleats remain on the surface of the ingot.

The ring 13 employed in the apparatus herein proposed eliminates theabove mentioned defects. The electromagnetic field of the inductor 1induces within this ring eddy currents whose magnetic field, wheninteracting with the inductor field, lowers the intensity of themagnetic field in the upper portion of the ingot. This results in adecrease in the intensity of movement of the flows of metal, thuseliminating the possibility of formation of defects on the ingotsurface.

The above-described apparatus has been tested in industrial conditions.

The produced ingots have had predetermined dimensions and shape and asmooth even surface.

What is claimed is:

1. An apparatus for continuous and semicontinuous casting of metalscomprising in combination: a device for uniform supply of molten metal,a ring-shaped electromagnetic inductor located under said device formaintaining 21 column of molten metal, an electromagnetic screen locatedinside said inductor and arranged coaxially therewith, said screenconsisting of a closed ring of a nonmagnetic metal and having anupwardly increasing thickness while the lower edge thereof is located atapproximately half of the inductor height, said increasing thicknessbeing such as to distribute the magnetic field of said inductor toprovide substantial equality between the hydrostatic and electromagneticpressures exerted along said column of molten metal, means for supplyinga cooling medium into the gap between said inductor and the lateralsurface of said column, and means for supporting and progressivelylowering said column as 'it cools and solidifies.

2. An apparatus as. claimed in claim 1, comprising a ring made of ametal having high; electric conduction located inside theelectromagnetic screen in its upper portion, ,said ring being disposedconcentrically with said screen, close to it, and with means for movingit along a vertical line.

References Cited UNITED STATES PATENTS 3,467,166 9/1969 Getselev et a1164-250X ROBERT D. BALDWIN, Primary Examiner U.S. C1. X.R.

